1. Technical Field of the Invention
This invention relates generally to communication systems and more particularly to a transformer that may be used in such communication systems.
2. Description of Related Art
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), radio frequency identification (RFID), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, RFID reader, RFID tag, et cetera communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system or a particular RF frequency for some systems) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the Internet, and/or via some other wide area network.
For each wireless communication device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the receiver is coupled to the antenna and includes a low noise amplifier, one or more intermediate frequency stages, a filtering stage, and a data recovery stage. The low noise amplifier receives inbound RF signals via the antenna and amplifies then. The one or more intermediate frequency stages mix the amplified RF signals with one or more local oscillations to convert the amplified RF signal into baseband signals or intermediate frequency (IF) signals. The filtering stage filters the baseband signals or the IF signals to attenuate unwanted out of band signals to produce filtered signals. The data recovery stage recovers raw data from the filtered signals in accordance with the particular wireless communication standard.
As is also known, the transmitter includes a data modulation stage, one or more intermediate frequency stages, and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with a particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna.
In many wireless communication devices, the transmitter and/or receiver is coupled to antenna, or antennas, by one or more transformers. Such a transformer typically includes a single-ended winding that is coupled to the antenna and a differential winding that is coupled to a low noise amplifier of a receiver section and/or to a power amplifier of a transmitter section. The transformer may be implemented in a variety of ways. For instance, the transformer may be implemented on-chip with the receiver and/or transmitter section. While an on-chip transformer provides the convenience of not requiring an external transformer, the on-chip transformer's power capabilities are limited due to its size.
Another known implementation of a transformer is a marginal type transformer that is fabricated on a printed circuit board (PCB). A marginal type transformer includes two parallel traces that each is approximately one-quarter wavelength in length. As such, a margin type transformer consumes a significant amount of PCB real estate, but does provide significant power in comparison to the on-chip transformer. As with any transformer, impedance matching between the antenna and receiver or transmitter section is an important design criterion.
In addition to the above uses, transformers are used in a multitude of applications that require an AC voltage to be converted from one level to another with an electrical isolation between the windings. For example, almost all power converters (AC to DC, DC to DC, and DC to AC) include a transformer for a voltage level shift. Typically, the transformer includes a primary winding wrapped around a ferrite core with a secondary winding wrapped around another part of the ferrite core or over the primary winding.
In all of the transformers discussed above, i.e., on-chip transformers, on-PCB transformers, ferrite core transformers, and other types of transformers (e.g., air core), they have a similar construction technique for the primary and secondary windings. For example, the on-chip transformers have both windings fabricated on a die of an integrated circuit. While such transformers offer a wide variety of applications, there are emerging applications that would benefit from a transformer having one of its winding implemented on a die of an integrated circuit while the other winding is implemented off of the die.
Therefore a need exists for a transformer that has one winding implemented on a die of an integrated circuit and another winding implemented off of the die.